LH1306 is an inhibitor of the interaction between programmed cell death 1 (PD-1) and its ligand PD-L1 that has an IC50 value of 25 nM in a homologous time-resolved fluorescence (HTRF) assay.1 It increases the activation of Jurkat cells expressing PD-1 in co-culture with U2OS or CHO cells expressing PD-L1 (EC50s = 334 and 4,214 nM, respectively, in reporter assays).